Unable to send whole file over TCP connection! (UNIX C) - c

Question

So I programmed a multi threaded web server, here is one function from the program. This function takes output file descriptor (fd), content type, pointer to data to be served (*buf) and size of the data (numbytes). It always gets stuck at 5775 bytes! I've tried using write() instead of send(), but no avail! I tried to send whole buf at a time, and even tried to transfer it in chunks, but wget shows that it gets stck at 5775 bytes! Here is the code:
int return_result(int fd, char *content_type, char *buf, int numbytes)
{
char out_buf[BUF_SIZE], numb[6];
int buf_len, total = 0, buf_size;
long int i = 0;
sprintf(numb, "%d", numbytes);
strcpy(out_buf, "HTTP/1.1 200 OK \nContent-Type: ");
strcat(out_buf, content_type);
strcat(out_buf, "\nContent-Length: ");
strcat(out_buf, numb);
strcat(out_buf, "\nConnection: Close\n \n");
printf("\nSending HTTP Header\n %d bytes sent!",
send(fd, out_buf, strlen(out_buf), 0));
char *start = NULL, *str = NULL, *temp = NULL;
start = buf;
printf("\n Start Pointer Val = %ld", &start);
while (start != NULL) {
printf("\n While Loop");
if (i + 2048 * sizeof(char) < numbytes) {
printf("\n If 1");
str = (char *)malloc(sizeof(char) * 2048);
memcpy(str, start, sizeof(char) * 2048);
i = i + 2048 * sizeof(char);
buf_size = send(fd, str, 2048, 0);
free(str);
printf("\n Sent %d bytes total : %d", buf_size, total =
total + buf_size);
temp = start + sizeof(char) * 2048;
start = temp;
} else {
i = numbytes - i * sizeof(char);
if (i > 0) {
printf("\n If 2");
printf("\n Value of i %d", i);
str = (char *)malloc(sizeof(char) * i);
memcpy(str, start, sizeof(char) * i);
printf("Total bytes finally sent:%d", total =
total + send(fd, str, i, 0));
if (total == numbytes) {
printf("\nTransfer Complete!");
}
free(str);
}
start = NULL;
}
}
printf("out of loop!");
return 0;
}

Answer 1

I'd like to suggest replacing your code with the following writen() function from Advanced Programming in the Unix Environment, 2nd edition:
ssize_t /* Write "n" bytes to a descriptor */
writen(int fd, const void *ptr, size_t n)
{
size_t nleft;
ssize_t nwritten;
nleft = n;
while (nleft > 0) {
if ((nwritten = write(fd, ptr, nleft)) < 0) {
if (nleft == n)
return(-1); /* error, return -1 */
else
break; /* error, return amount written so far */
} else if (nwritten == 0) {
break;
}
nleft -= nwritten;
ptr += nwritten;
}
return(n - nleft); /* return >= 0 */
}
This code is already debugged and known working, and further allows write(2) to write PIPE_BUF bytes at a go for better speed when things are working well.
send(2) should block if it cannot send all the data you have requested, though. I think more interesting would be debugging the version with plain send(2) without any of the surrounding efforts to break things into blocks.
Better than both write(2) and send(2) would be sendfile(2) -- open the file, pass the descriptor and socket to sendfile(2), and let the kernel handle it all for you, using zero-copy mechanisms if possible.
One last point: HTTP uses CRLF, not plain carriage returns. Each \n should be replaced with \r\n.

Answer 2

Try something like this (printf() statements omitted for clarity):
int send_buf(in fd, void *buf, int numbytes)
{
char *start = (char*) buf;
while (numbytes > 0)
{
int sent = send(fd, start, numbytes, 0);
if (sent <= 0)
{
if ((sent == -1) && (errno == EAGAIN))
{
fd_set wfds;
FD_ZERO(&wfds);
FD_SET(fd, &wfds);
if (select(fd + 1, NULL, &wfds, NULL, NULL) == 1)
continue;
}
return -1;
}
start += sent;
numbytes -= sent;
}
return 0;
}
int return_result(int fd, char *content_type, void *buf, int numbytes)
{
char out_buf[BUF_SIZE],
int len = sprintf(out_buf,
"HTTP/1.1 200 OK\r\n"
"Content-Type: %s\r\n"
"Content-Length: %d\r\n"
"Connection: Close\r\n"
"\r\n",
content_type,
numb);
if (send_buf(fd, out_buf, len) != 0)
return -1;
if (send_buf(fd, buf, numbytes) != 0)
return -1;
return 0;
}